In 2006, agents of Al Qaeda, as well as those inspired by its ideology, continued their attacks. Violence in Iraq intensified, and Afghanistan saw its most violent year since 2001.

Despite worsening chaos on those fronts, counterterrorist forces arrested and killed high-profile terrorists and kept the West free from attack. But these actions don't appear to have weakened the appeal of Al Qaeda's agenda. "Home-grown" militants around the world joined its jihad, as regional fighting heightened perceptions of a global war on Islam.

Here's an assessment of some of the most significant gains and losses for Al Qaeda last year:

Terrorism experts say that militant jihadists shifted focus to the original Al Qaeda base to utilize experience and tactics gained in Iraq – as reflected in the increase in suicide bombings from 27 in 2005 to 139 in 2006, according to US estimates. Al Qaeda leader Osama bin Laden and his No. 2, Ayman al-Zawahiri, are widely believed to be hiding in the border region between Afghanistan and Pakistan.

Algeria's Salafist Group for Preaching and Combat declared an alliance with Al Qaeda in September.

Britain

In August, authorities foiled a terrorist plot with all the hallmarks of an Al Qaeda attack. British security arrested dozens of suspects whom they allege were participating in a plan to bomb up to 10 passenger flights from England to the US.

But Europe's major problem in 2006, experts say, was "home-grown terrorism." Britain's spy chief, Eliza Manningham-Buller, warned in November that the security service MI5 was "working to contend with some 200 groupings or networks, totaling over 1,600 identified individuals."

Europe is a primary recruiting base for Al Qaeda as Muslim communities there have access to wealth and freedom of movement, says Rohan Gunaratna, author of "Inside Al Qaeda: Global Network of Terror."

Islamic militants are "busy recruiting from the Muslim diaspora," adds Paul Wilkinson, chairman of the advisory board of the Centre for the Study of Terrorism and Political Violence at the University of St. Andrews in Scotland. "It's very clear that the organization is still very much in business.... And that recruitment has been going on quite rapidly."

Egypt

An April 24 attack in a Sinai resort town was not claimed by Mr. bin Laden, but the hotel bombings had many similarities to an Al Qaeda strike. The attacks were a sign that the group's tactics have gained a foothold among other radical groups.

Indonesia

Hundreds of members of Jemaah Islamiyah (JI), a major terrorist group linked to Al Qaeda, were arrested, while more radical members split from the group in early 2006 to form Tanzim Qaedat al-Jihad. The biggest blow to counterterrorism efforts was the release of Abu Bakar Bashir from jail in June 2006 after he spent 26 months in prison. The radical Islamic cleric, who is said to lead JI, was cleared of conspiracy charges in December for his role in the 2002 Bali hotel bombings. "Indonesian counterterrorism law is gravely weak," says Mr. Gunaratna. "Abu Bakar Bashir is the leader of the most dangerous group in Southeast Asia. His group has killed more than 250 people."

Iraq

The most violent offshoot of bin Laden's global organization, Al Qaeda in Iraq, seemed to suffer a major blow in 2006 with the killing of former chief Abu Musab al-Zarqawi in June.

But the loss of his leadership may have actually strengthened the group, says Gunaratna. "Zarqawi was a very able and ruthless man," he says, but "not a politician." His successor, Abu Ayyub al-Masri, "is following exactly the instructions of bin Laden and al-Zawahiri."

Al Qaeda in Iraq is small but vicious, says Gunaratna. It was linked to the February bombing of a Shiite shrine in Samarra – the impact of which ratcheted up sectarian killings in 2006.

In January, the UN said that more than 34,000 Iraqi civilians were killed last year, most in Sunni-Shiite violence that Al Qaeda is bent on fomenting.

Pakistan

In September 2006, President Pervez Musharraf arranged his most recent peace deal with pro-Taliban militants in Pakistan's remote Federally Administered Tribal Areas along the Afghan border. Mr. Musharraf's peace-brokering, critics warn, has allowed the Taliban to move freely between Afghanistan and Pakistan. John Negroponte, the first director of national intelligence who is expected to be confirmed as deputy secretary of state, said that the deal is allowing Al Qaeda operatives to reorganize in the area and to cultivate "stronger operational connections and relationships that radiate outward from their leaders' secure hideout in Pakistan to affiliates throughout the Middle East, North Africa, and Europe."

Palestinian territories

In March, Israel for the first time charged two Palestinians for being members of a group possibly connected to Al Qaeda. Journalist kidnappings raised concerns that the group was infiltrating the territory or inspiring copycats.

Philippines

The Philippine military killed two top members of the Al Qaeda-linked militant group Abu Sayyaf. Military officials say that the killing of the group's leader, Khadaffy Janjalani, in September 2006, and his deputy Abu Sulaiman, who was killed in January 2007, have rendered the group ineffective. Still, US-trained Philippine soldiers continue to regularly engage Abu Sayyaf militants.

Saudi Arabia

In February, Saudi Arabia thwarted a bombing on an oil-processing plant. Raids and gun battles throughout the country netted more than 100 suspected Al Qaeda militants, but US officials have said that the kingdom could do more to curb terrorism, including stopping the flow of militants and funds across its borders.

Somalia

In June, Islamists suspected of harboring key Al Qaeda operatives overran Mogadishu and took over most of the country except Baidoa, the seat of a weak transitional government. US-backed warlords could not stop the Union of Islamic Courts, which denies charges of ties with Al Qaeda. The country saw its first suicide bombing – which Somali officials blamed on Al Qaeda – on Sept. 19, a failed attempt to kill the interim president. The Islamists fled in the wake of an Ethiopian and Somali offensive that began Dec. 26.

USA

North America saw no Al Qaeda attacks. American security forces working around the world have seen "an awful lot of victories," says Arnaud de Borchgrave, director of the Transnational Threats Project at the Center for Strategic and International Studies in Washington. "The CIA has carte blanche to track terrorists around the world," he says. Critics say that this has led to the use of secret prisons used to interrogate Al Qaeda suspects.

On the domestic front, officials say that they thwarted attacks on Chicago's Sears Tower and New York's transit system over the summer and arrested several people in the process – although it was unclear how serious such plans were.

Yemen

Yemen prevented bomb attacks at two oil facilities on Sept. 15 that were, according to intelligence consulting firm Stratfor, probably commissioned by Al Qaeda. Twenty-three suspected Al Qaeda fighters escaped from prison in February. The government killed or captured many of them, but officials say that those remaining may help Al Qaeda in Yemen to regroup.